Devices and Methods for Duplexer Loss Reduction

ABSTRACT

Methods and devices are described for reducing transmit RF signal loss in a bi-directional RF transmit/receive system with a duplexer circuit. In one case a filter in a transmit path is used such as to reduce amplified noise in a receive frequency band.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. patent application Ser. No. ______ entitled “Methods for Increasing RF Throughput Via Usage of Tunable Filters” (Attorney Docket No. PER-099-PAP) filed on even date herewith and incorporated herein by reference in its entirety. The present application is also related to U.S. patent application Ser. No. ______ entitled “Integrated Tunable Filter Architecture” (Attorney Docket No. PER-115-PAP) filed on even date herewith and incorporated herein by reference in its entirety.

The present application may be related to U.S. patent application Ser. No. 13/797,779 entitled “Scalable Periphery Tunable Matching Power Amplifier”, filed on Mar. 3, 2013, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to International Application No. PCT/US2009/001358, entitled “Method and Apparatus for use in digitally tuning a capacitor in an integrated circuit device”, filed on Mar. 2, 2009, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to U.S. patent application Ser. No. 13/595,893, entitled “Method and Apparatus for Use in Tuning Reactance in a Circuit Device”, filed on Aug. 27, 2012, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to U.S. patent application Ser. No. 14/042,312, filed on Sep. 30, 2013, entitled “Methods and Devices for Impedance Matching in Power Amplifier Circuits”, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to U.S. Pat. No. 7,248,120, issued on Jul. 24, 2007, entitled “Stacked Transistor Method and Apparatus”, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to U.S. patent application Ser. No. 13/828,121, filed on Mar. 14, 2013, entitled “Autonomous Power Amplifier Optimization”, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to U.S. patent application Ser. No. 13/967,866 entitled “Tunable Impedance Matching Network”, filed on Aug. 15, 2013, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to U.S. patent application Ser. No. 13/797,686 entitled “Variable Impedance Match and Variable Harmonic Terminations for Different Modes and Frequency Bands”, filed on Mar. 12, 2013, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to U.S. patent application Ser. No. 14/042,331 entitled “Methods and Devices for Thermal Control in Power Amplifier Circuits”, filed on Sep. 30, 2013, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to U.S. patent application Ser. No. 13/829,946 entitled “Amplifier Dynamic Bias Adjustment for Envelope Tracking, filed on Mar. 14, 2013, the disclosure of which is incorporated herein by reference in its entirety. The present application may also be related to US patent application Ser. No. 13/830,555 entitled “Control Systems and Methods for Power Amplifiers Operating in Envelope Tracking Mode”, filed on Mar. 14, 2013, the disclosure of which is incorporated herein in its entirety.

BACKGROUND

1. Field

The present teachings relate to RF (radio frequency) circuits. More particularly, the present teachings relate to methods and apparatuses for reducing duplexer loss in an RF transmit path.

2. Description of Related Art

Radio frequency (RF) devices, such as cell phone transmitters, are becoming increasingly complex due to additional frequency bands, more complex modulation schemes, higher modulation bandwidths, and the introduction of data throughput improvement schemes such as simultaneous RF transmission and/or reception within a same or different, but closely spaced, bands or channels within a band (e.g. voice, data), and aggregate transmission wherein information is multiplexed over parallel RF transmissions. Due to the closely spaced transmit/receive frequency bands/channels of a front-end stage used in such RF devices, burden on a duplexer design used in such RF devices has increased, where associated sharp band-pass filters can isolate an RF signal being transmitted from a receive path at the cost of attenuating the RF signal being transmitted.

SUMMARY

According to a first aspect of the present disclosure, a radio frequency (RF) circuital arrangement is presented, the arrangement comprising: an RF transmit path comprising: a plurality of cascaded amplifiers configured, during operation of the circuital arrangement, to amplify a transmit RF signal, the transmit RF signal operating over a first frequency band, and a first filter placed between two consecutive amplifiers of the plurality of cascaded amplifiers, the first filter configured during operation of the circuital arrangement, to attenuate a second frequency hand different from the first frequency band, and pass the first frequency band; an RF receive path configured, during operation of the circuital arrangement, to receive a receive RF signal over the second frequency band, and a bi-directional transmit/receive circuit connected to the RF transmit path and to the RF receive path, the bi-directional transmit/receive circuit comprising: a second filter configured, during operation of the circuital arrangement, to pass the first frequency band and to attenuate the second frequency band.

According to second aspect of the present disclosure, a method for reducing loss of a transmit RF signal in a duplexer unit of an radio frequency (RF) transmit/receive system, the method comprising: providing an RF transmit path comprising a plurality of cascaded amplifiers; inserting, in-between two amplifiers of the plurality of cascaded amplifiers, a first filter; based on the inserting, attenuating a receive frequency band and passing a transmit frequency band; based on the attenuating, relaxing design parameters of a second filter of a duplexer unit, the second filter being configured to pass the transmit frequency band and to attenuate the receive frequency band; based on the relaxing, reducing a number of filter stages of the second filter, and based on the reducing, reducing an attenuation at the transmit frequency band through the second filter of the duplexer unit.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the present disclosure and, together with the description of example embodiments, serve to explain the principles and implementations of the disclosure.

FIG. 1 shows an exemplary block diagram of a transmit/receive system comprising a transmit path and a receive path of an RF front-end stage of an RF device, as used, for example, in a cellular phone.

FIG. 2 shows an exemplary embodiment according to the present disclosure of a transmit/receive system comprising a filter in a transmit path.

FIGS. 3A-3C and FIGS. 4A-4C show various exemplary embodiments according to the present disclosure of a shape of the filter in the transmit path of FIG. 2.

FIG. 5 shows a graphical representation of analysis performed on the transmit path of FIG. 2 when using the filter in-between amplification stages, as depicted in FIG. 2.

DETAILED DESCRIPTION

Throughout this description, embodiments and variations are described for the purpose of illustrating uses and implementations of the inventive concept. The illustrative description should be understood as presenting examples of the inventive concept, rather than as limiting the scope of the concept as disclosed herein.

The present disclosure describes electrical circuits in electronics devices (e.g., cell phones, radios) having a plurality of devices, such as for example, transistors (e.g., MOSFETs). Persons skilled in the art will appreciate that such electrical circuits comprising transistors can be arranged as amplifiers. As described in a previous disclosure (U.S. patent application Ser. No. 13/797,779, incorporated herein by reference in its entirety), a plurality of such amplifiers can be arranged in a so-called “scalable periphery” (SP) architecture of amplifiers where a total number (e.g., 64) of amplifier segments are provided. Depending on the specific requirements of an application, the number of active devices (e.g., 64, 32, etc.), or a portion of the total number of amplifiers (e.g. 1/64, 2/64, 40% of 64, etc. . . . ), can be changed for each application. For example, in some instances, the electronic device may desire to output a certain amount of power, which in turn, may require 32 of 64 SP amplifier segments to be used. In yet another application of the electronic device, a lower amount of output power may be desired, in which case, for example, only 16 of 64 SP amplifier segments are used. According to some embodiments, the number of amplifier segments used can be inferred by a nominal desired output power as a function of the maximum output power (e.g. when all the segments are activated). For example, if 30% of the maximum output power is desired, then a portion of the total amplifier segments corresponding to 30% of the total number of segments can be enabled. The scalable periphery amplifier devices can be connected to corresponding impedance matching circuits. The number of amplifier segments of the scalable periphery amplifier device that are turned on or turned off at a given moment can be according to a modulation applied to an input RF signal, a desired output power, a desired linearity requirement of the amplifier or any number of other requirements.

The term “amplifier” as used in the present disclosure is intended to refer to amplifiers comprising single or stacked transistors configured as amplifiers, and can be used interchangeably with the term “power amplifier (PA)”. Such terms can refer to a device that is configured to amplify a signal input to the device to produce an output signal of greater magnitude than the magnitude of the input signal. Stacked transistor amplifiers are described for example in U.S. Pat. No. 7,248,120, issued on Jul. 24, 2007, entitled “Stacked Transistor Method and Apparatus”, the disclosure of which is incorporated herein by reference in its entirety. Such amplifier and power amplifiers can be applicable to amplifiers and power amplifiers of any stages (e.g., pre-driver, driver, final), known to those skilled in the art.

As used in the present disclosure, the term “mode” can refer to a wireless standard and its attendant modulation and coding scheme or schemes. As different modes may require different modulation schemes, these may affect required channel bandwidth as well as affect the peak-to-average-ratio (PAR), also referred to as peak-to-average-power-ratio (PAPR), as well as other parameters known to the skilled person. Examples of wireless standards include Global System for Mobile Communications (GSM), code division multiple access (CDMA), Worldwide Interoperability for Microwave Access (WiMAX), Long Term Evolution (LTE), as well as other wireless standards identifiable to a person skilled in the art. Examples of modulation and coding schemes include binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), quadrature amplitude modulation (QAM), 8-QAM, 64-QAM, as well as other modulation and coding schemes identifiable to a person skilled in the art.

As used in the present disclosure, the term “band” can refer to a frequency range. More in particular, the term “band” as used herein refers to a frequency range that can be defined by a wireless standard such as, but not limited to, wideband code division multiple access (WCDMA) and long term evolution (LTE).

As used in the present disclosure, the term “channel” can refer to a frequency range. More in particular, the term “channel” as used herein refers to a frequency range within a band. As such, a band can comprise several channels used to transmit/receive a same wireless standard.

As used in the present disclosure, the term “notch filter” can refer to a band-stop filter, also known as a band-rejection filter or a band-reject filter, with a narrow stopband. Such tilter passes most frequencies unaltered (e.g. without attenuation) and attenuates only those frequencies in a specific frequency range defined by the stopband.

FIG. 1 shows a block diagram of a bi-directional transmit/receive communication system (100) comprising a transmit path and a receive path which can be used in a multi-band and multi-channel RF front-end stage of an RF device, such as, for example, a cellular phone. The transmit/receive system (100) of FIG. 1 comprises a transceiver unit (105) adapted to generate an RF signal to be transmitted via an antenna (120) of the system. An RF transmit path of the transmit/receive system (100) can comprise an RF amplification stage comprising a driver stage (150) and a final stage (160), and a duplexer unit (110). The RF amplification stage (150+160) can amplify the RF signal provided by the transceiver unit (105) and further shape the RF signal in a way more suitable for transmission, such as described in, for example, U.S. patent application Ser. No. 13/829,946 and U.S. patent application Ser. No. 13/830,555, whose disclosures are incorporated herein by reference in their entirety. Furthermore, as known to the person skilled in the art, the amplification stage (e.g. 150+160) can comprise one or more (e.g. 3, 4, . . . ) series connected (e.g. cascaded) amplifiers, such as the driver (150) and the final (160), wherein each of the series connected amplifiers may further comprise stacked transistors such as described in, for example, U.S. Pat. No. 7,248,120, incorporated herein by reference in its entirety, and/or parallel amplifiers such as scalable periphery amplifiers, as described in, for example, U.S. patent application Ser. No. 13/797,779, incorporated herein by reference in its entirety and/or efficiency improvement amplifiers such as envelope tracking amplifiers, as described in U.S. patent application Ser. No. 13/829,946, incorporated herein by reference in its entirety. Furthermore, the various series connected (e.g. cascaded) amplifiers (e.g. 150, 160) may further be coupled via impedance matching and/or harmonic termination networks, as described in, for example, U.S. patent application Ser. No. 13/967,866 and U.S. patent application Ser. No. 13/797,686, incorporated herein by reference in its entirety.

In the circuital arrangement of FIG. 1, an RF signal amplified via the amplification stage (150+160) is fed to the duplexer unit (110), which duplexer unit further filters the RF signal to be transmitted through a band-pass filter (130) centered at a frequency (fi) of operation of the band within which the RF signal is transmitted. The duplexer unit (130) can allow simultaneous transmit and receive via a same antenna (120) by filtering the transmit RF signal such as not to affect (e.g. overload) a receive RF signal to the receive path and filtering a receive RF signal, via a receive band-pass filter (140), according to a receive frequency band and channel (e.g. at a center frequency f_(R)). A received RF signal, subsequent to filtering by the duplexer (110), can be fed to the transceiver unit (105) via an internal amplifier (e.g. low noise amplifier) which is tuned for the frequency of the received RF signal and has an input stage closely matched to the receive path electrical characteristics (e.g. impedance) at the tuned frequency. Once the received RF signal is amplified, the transceiver unit (105) can further down convert the received amplified signal to an intermediate frequency (IF) signal used for decoding of the information (e.g. voice, data) in the received RF signal.

The person skilled in the art readily knows that the bi-directional communication system, such as the transmit/receive system (100) of FIG. 1, the duplexer (110) is used to isolate the receiver from the transmitter while permitting the two channels to use the common antenna (120). Via its built in filters, the duplexer provides adequate rejection of transmitter noise occurring at the receive frequency band and must provide sufficient isolation between the receive and transmit channels such as to prevent receiver desensitization (e.g. overload via residual transmit RF signal and/or associated noise).

The person skilled in the art further knows that any electronic device, such as the amplifier (150, 160) of FIG. 1, generates some deterministic thermal noise at its input, a power of which can be given by the formula:

Noise_(power) =k·T·B·F _(n)  (1)

where k is the Boltzmann's constant, T is the operating temperature of the device, B is the bandwidth over which the thermal noise is being considered, and F_(n) is a constant noise factor (figure of merit). Such power associated to the thermal noise, as given by formula (1), at an input of an amplifier, can get amplified via the gain of the amplifier and can therefore produce an amplified noise (e.g. power, voltage) at the output of the amplifier which is a factor of G higher than the noise at the input of the amplifier, G being the gain of the amplifier over the frequency range of interest (e.g. determined by bandwidth B).

Therefore, in a configuration where a cascaded arrangement of amplifiers is used, such as the configuration depicted in FIG. 1 with amplifiers (150) and (160) being cascaded, power associated with thermal noise of an amplifier in the arrangement can get multiplied by each of the subsequent amplifiers. As such, a total power at the output of the cascaded amplifiers associated to the noise at the input of each amplifier, in a case where k amplifiers are cascaded, can be given by the expression:

Noise_(Total) =N ₁ ·G ₁ . . . G _(k) +N ₂ ·G ₂ . . . G _(k) + . . . +N _(k) ·G _(k)  (2)

where G₁ is the gain of the i^(th) amplifier of the cascaded k amplifiers, and N, is the input power associated to the thermal noise at the input of the i^(th) amplifier, as given by formula (1). According to the expression (2), a noise contributed by an amplifier further from the output of the cascaded arrangement of amplifiers (e.g. further from a duplexer) can have a greater impact on the total noise Noise_(Total) of the arrangement of cascaded amplifiers, as it gets amplified by a larger number of amplifiers. It should be noted that in the case where an RF signal is fed to such a cascaded arrangement of amplifiers, noise at the output of a corresponding amplifier, such as one in a transceiver unit (105) of FIG. 1 which feeds an RF signal to the transmit path, gets added to the input thermal noise of the first amplifier in the arrangement. Therefore, in the particular case of the first amplifier in the arrangement, we can have:

N ₁ =N _(xcvr) +k·T·B·F _(n1)  (3)

where N_(xcvr) is a contributing noise power from the transceiver unit (e.g. 105 of FIG. 1).

Therefore, for the particular case of the two-stage cascaded arrangement of FIG. 1 comprising a driver amplifier (150) and a final amplifier (160), the overall noise at the output of the arrangement can be represented by the expression:

Noise=(N _(xcvr) +k·T·B·F _(driver))·G _(driver) ·G _(final) +k·T·B·F _(final) ·G _(final)  (4)

Such noise can be defined as the transmit channel noise of the transmit/receive system (100) of FIG. 1 and can be present at an input terminal of the duplexer (110) connected to the transmit path (e.g. amplifier 160).

A duplexer, such as duplexer (110) of FIG. 1, comprises two sharp band-pass filters (e.g. opposite of notch filters) (130, 140), a transmit filter (130) within the transmit path (center frequency at f_(T)), and a receive filter (140) within the receive path (center frequency at f_(R)). The transmit filter (130) needs to attenuate transmit (Tx) channel noise (e.g. as per expressions (4) above) at the receiver frequency band, so not to desensitize the receiver circuitry, as a power associated to the transmit channel noise as provided by (4) can be higher than a power of a receive signal at the antenna (120). Due to the high gain of the combination of driver/final amplifiers (150/160) in the transmission channel, which not only amplifies the transmission signal but also the thermal noise within electronic elements in the transmit path as well as the noise at the output stage of the transceiver unit (105), commonly a greater than about 35 dB attenuation in the receive frequency band is desired for the transmit filter (130) design to attenuate the receive band noise of the transmit path, although a preferred value can be in a range of 45-50 dB attenuation. Due to the desired performance (e.g. greater than about 35 dB attenuation in a narrow frequency band) and the associated frequency range (e.g. center frequency of several GHz), such filters (e.g. transmit filter 130) are typically chosen to be surface acoustic wave (SAW) or bulk acoustic wave (BAW) filters as opposed to the simpler RLC filters. Furthermore, the stringent filter design requirement (e.g. large rejection at the vicinity of the pass hand) of the transmit filter (130) can create some undesirable transmit signal loss at the output (e.g. attenuation within the Tx frequency band, insertion loss) which can be greater than about 2 dB. Reducing the amplitude (e.g. power) of the transmit channel noise in the Rx frequency band, allows for a more relaxed design of the filter (130) (e.g. less attenuation/rejection required at the Rx frequency band) and thus can reduce the amount of the transmission signal loss due to the (transmit) filter (130) of the duplexer (110), and can also allow usage of a simpler RLC filter (e.g. a filter comprising one or more shunt and/or series RLC stages) in lieu of the SAW/BAW filter. The skilled person readily knows that relaxing design parameters of the filter (130) can reduce the number of stages (e.g. resonant stages) the filter contains and therefore reduce the insertion loss (e.g. attenuation) of the filter, as each stage can increase the insertion loss of the filter. It follows that according to an embodiment of the present disclosure, transmit channel noise at a frequency band of the receive channel can be reduced by using a filter which is configured to attenuate the receive frequency band while not affecting (e.g. having a minimum impact on) the transmit frequency band. Such a band-attenuating filter can be one of several types of filters known to a person skilled in the art, which type can depend on a relative position, within a frequency spectrum, of the receive and transmit frequency bands, as further explained in the ensuing paragraphs.

According to an embodiment of the present disclosure, by inserting a filter (270) (e.g. a band-reject filter, low-pass filter, high-pass filter, notch filter, etc. . . . ), designed to attenuate the receive frequency band centered at the receive center frequency f_(R), in-between the driver stage (150) and the final stage (160), as depicted in the bi-directional transmit/receive communication system (200) of FIG. 2, transmit channel noise at the receive frequency band, contributed by the driver stage (150) and the associated gain (e.g. as per expression (4) above), is reduced without affecting the transmit (Tx) channel which operates at a center frequency f_(T) different from f_(R). Such reduction (e.g. power attenuation) can be expressed by the expression:

Noise=(N _(xcvr) +k·T·B·F _(driver))·G _(driver) ·A _(int) ·G _(final) +k·T·B·F _(final) ·G _(final)  (5)

where A_(int) is the attenuation provided by the inter-stage (e.g. positioned between two amplification stages of the cascaded arrangement of amplifiers) filter (270) within the receive frequency band.

According to some embodiments of the present disclosure, such attenuation provided by the filter (270) can be in a range of about 10-25 dB (e.g. greater than about 10 dB). The person skilled in the art will appreciate the advantage of lowering such noise (e.g. by greater than about 10 dB) has on the design of the transmit filter (130) which can subsequently be designed with more relaxed design parameters. In turn and according to an embodiment of the present disclosure, a more relaxed transmit filter (130) design can reduce the amount of attenuation within the transmit frequency band (e.g. insertion loss) for an improvement in transmit RF signal power. For example, a typical 2-3 dB insertion loss (e.g. attenuation within the transmit frequency band) provided by a typical transmit filter (130) (e.g. SAW/BAW filter) of a duplexer unit (110) can be reduced to half or to about 1-1.5 dB after relaxing the transmit filter design per the provided embodiment according to the present disclosure. Relaxing of the transmit filter design can in some instances reduce the insertion loss to a value which is less than about 2 dB, and still providing a benefit over the typical larger than about 2 dB insertion loss of a transmit filter (130) implemented using SAW/BAW filters. The person skilled in the art will appreciate the impact of this reduction in terms of a corresponding power amplifier (PA) efficiency, as a 0.1 dB reduction in (RF signal) attenuation can increase PA efficiency by about 1% or equivalent to 10 mA reduction of current drain fir a cell phone with a 28 dBm output. Further, a relaxed design of the transmit filter (130) can also allow for fewer stages in the design of the filter, thus fewer components for a reduction in effective size of the filter. According to further embodiments of the present disclosure and due to the relaxed design requirements of the transmit filter (130), such filter can be designed using standard RLC filter design techniques known to the skilled person, and therefore providing some cost benefits over the typical SAW/BAW filter implementation as well as possibility for monolithic integration of the filter within a duplexer integrated circuit (IC) or other.

A typical range for the gain of the final amplifier stage (160) can be 10-20 dB. A typical noise figure of the final stage can be less than 10 dB. FIG. 5 shows a graphical representation of analysis performed on the transmit path when using an inter-stage filter (270) between the driver amplifier (150) and the final amplifier (160). The graph of FIG. 5 is based on expression (5) and a set of assumptions as represented by the Table 1 below. The set of assumptions contained in Table 1, show typical and desired values for the various operating parameters of the transmit/receive system (200) of FIG. 2. Based on the graph depicted in FIG. 5, the person skilled in the art will recognize that a preferred value for a gain of the final stage when considering loss (e.g. attenuation) of the duplexer (130) and loss of the inter-stage filter (270) can be in the range of 12-14 dB. As depicted by the graph of FIG. 5, when the final stage gain is in the range of 12-14 dB, a higher efficiency improvement for a transmitted signal at the output of the duplexer (130) can be obtained. The graph, and corresponding tabulated data, show that when the final amplifier stage gain is reduced to a certain level, then higher power can be lost in the inter-stage filter, while increasing the final stage gain to a certain level, can limit the amount of relaxation of the duplexer attenuation. The noise figure of the final amplifier stage (160) should be as low as possible for optimum improvement in efficiency when using the inter-stage filter (160). A noise figure of less than 5 dB is reasonable and used within the set of assumptions associated to the graph of FIG. 5. Furthermore, it can be desired that the attenuation of the inter-stage filter (270) is such as to attenuate the receive band noise by an amount greater than or equal to (N_(xcvr)+F_(driver))·G_(driver) for the improvement (e.g. via insertion of the inter-stage filter) to have maximum effect. Such attenuation can get the noise level into the final amplifier stage (160) down to the thermal noise level.

TABLE 1 Assumptions in the Analysis: Gtotal 30 dB Pout 0.8 W NFdriver 5 dB PAE PA 40% NFfinal 5 dB nominal duplexer loss 2.2 dB noise xcvr −168.4 dBm/Hz nominal duplexer noise 45 dB attenuation kT −174.4 dBm/Hz notch IL 1.5 dB

Attenuation at the receive frequency band per the various embodiments of the present disclosure can be performed by the filter (270) as depicted in FIG. 2. Design parameters of such filter can be such as to attenuate a signal at a frequency within the receive frequency band while passing unaltered (e.g. no or minimum attenuation) a signal at a frequency within the transmit frequency band. As such, the receive band is attenuated and the transmit band is substantially unaltered. In this case, substantially unaltered can mean a power loss due to insertion of the filter within the transmit path of less than 2 dB. It should be noted that such loss in front of the final amplifier stage (160) has a lesser effect on efficiency than a loss at the output of the final amplifier stage (160).

FIGS. 3A-3C show a frequency map comprising a frequency content of the receive band (310) centered around the receive band center frequency f_(R), and a frequency content of the transmit band (320) centered around the transmit band center frequency f_(T), for the case where the frequency f_(T) is higher than the frequency f_(R). It should be noted that elements (310) and (320) of FIGS. 3A-3C are only relevant per their attributes with respect to the frequency content (e.g. X-axis of the frequency map). Superimposed with the described frequency map. FIGS. 3A-3C also contain a frequency response (350 a-350 c) of the filter (270) of FIG. 2 which is described in the previous sections of the present disclosure. According to the various embodiments of the present disclosure and as depicted by FIGS. 3A-3C, the filter (270) can have a variety of frequency responses such as to satisfy its design requirements, which is to attenuate the receive band and to pass the transmit hand. According to the exemplary embodiment of the present disclosure as depicted in FIG. 3A, filter (270) can be designed as a high pass filter with a frequency response (350 a). Such high pass filter can be designed such as to comprise a cutoff frequency at a frequency between a higher frequency content of the receive band (310) and a lower frequency content of the transmit band (320) as depicted in FIG. 3A. Alternative exemplary frequency responses for the case where the frequency f_(T) is higher than the frequency f_(R) are depicted in FIGS. 3B and 3C, such as, for example, a wide band-reject filter with a frequency response of FIG. 3B and a narrow band-reject filter with a frequency response of FIG. 3C. The person skilled in the art can find other types of filter whose frequency responses attenuate signals within a region of the receive band (310) and pass signals within a region of the transmit band (320), such as, for example, a pass-band filter (e.g. FIG. 4B) passing a band comprising the transmit band (320) and stopping (e.g. attenuating) a region comprising the receive band (310). Therefore, the exemplary filter embodiments depicted in FIGS. 3A-3C should not be considered as limiting the scope of the teachings according to the present disclosure, but rather as exemplary embodiments of the inventive concept provided by those teachings.

Similar to FIGS. 3A-3C discussed in the prior section, FIGS. 4A-4C show a frequency map comprising a frequency content of the receive band (410) centered around the receive band center frequency f_(R), and a frequency content of the transmit band (420) centered around the transmit band center frequency f_(T), for the case where the frequency f_(T) is lower than the frequency f_(T). Superimposed with the described frequency map. FIGS. 4A-4C also contain a frequency response (450 a-450 c) of the filter (270) of FIG. 2 which is described in the previous sections of the present disclosure. According to the various embodiments of the present disclosure and as depicted by FIGS. 4A-4C, the filter (270) can have a variety of frequency responses such as to satisfy its design requirements, which is to attenuate the receive band and to pass the transmit band, such as, for example, a low-pass filter, a band-pass filter and a notch-filter whose frequency responses are represented in FIGS. 4A-4C by items (450 a-450 c) respectively. Realization of such filters represented by their frequency responses in FIGS. 3A-3C and FIGS. 4A-4C, using, for example, RLC networks or SAW/BAW, is beyond the scope of this disclosure and well within the ability of the person skilled in the art. Some example realizations of such filters are described, for example, in the referenced U.S. application Ser. No. ______ entitled “Integrated Tunable Filter Architecture” (Attorney Docket No. PER-115-PAP) filed on even date herewith and incorporated herein by reference in its entirety.

As previously mentioned, a transmit/receive RF signal can be in correspondence of a frequency band associated to a wireless standard (e.g. mode), and in turn, the frequency band can comprise a plurality of channels which can be used to transmit/receive an RF signal according the defined modulation scheme of the wireless standard. As it is known by the person skilled in the art, a same transmit/receive system, such as one depicted in FIG. 1 and FIG. 2, can be configured to operate over various modes (e.g. frequency, modulation). Accordingly and pursuant to a further embodiment of the present disclosure, the filter (270) of FIG. 2 with exemplary frequency response depicted in FIGS. 3A-3C and FIGS. 4A-4C can be a tunable filter (e.g. tunable low-pass filter, tunable high-pass filter, tunable band-reject filter, etc. . . . ), such as to allow tuning of a corresponding frequency response according to the various center frequencies corresponding to various modes of operation of the transmit/receive system (200) of FIG. 2, such as to maintain the design goal of passing an attending transmit frequency band (e.g. in correspondence of a transmit channel) while attenuating an attending receive frequency band (e.g. in correspondence of a receive channel). In such configuration, a signal-aware processor (e.g. controller) which knows of a current mode of operation of the system and a corresponding frequency band (e.g. transmit, receive), can control the tunable filter (270) to reject a receive frequency band while passing a transmit frequency band. An example of such signal-aware processor is the transceiver unit (105). As known to the person skilled in the art, such tunable filter (270) can comprise one or more stages (e.g. resistor-inductor-capacitor RLC) interconnected in a series and/or a shunt configuration and coupled and/or connected to the transmit path (e.g. between driver 150 and final 160) in a series and/or shunt configuration (series configuration shown in FIG. 2). Some examples of such filters connected in a shunt and/or series configuration are provided in the referenced U.S. application Ser. No. ______, entitled “Methods for Increasing RF Throughput Via Usage of Tunable Filters” (Attorney Docket No. PER-099-PAP) and U.S. application Ser. No. ______ entitled “Integrated Tunable Filter Architecture” (Attorney Docket No. PER-115-PAP), both filed on even date herewith and incorporated herein by reference in their entirety.

The system block diagram according to an embodiment of the present disclosure depicted in FIG. 2, is a simplistic representation of a single path transmit/receive system used in an RF front-end stage. Such front-end stage can include a plurality of similar transmit/receive paths sharing the same antenna (120), and the same transceiver unit (105). It follows that according to a further embodiments of the present disclosure, a similar filter (270) can be placed in a transmit path of each of the plurality of similar transmit/receive paths such as to reduce transmit channel noise over a corresponding receive frequency band and provide the same benefits as discussed in relation to the single transmit path and single receive path system (200) of FIG. 2.

The tunable filters described in the various embodiments according to the present disclosure can be constructed using one or more variable reactive elements, such as variable capacitors and variable inductors. Digitally tunable capacitors (DTC) and/or digitally tunable inductors, as described in, for example. International Application No. PCT/US2009/001358 and U.S. patent application Ser. No. 13/595,893, whose disclosures are incorporated herein by reference in their entirety, can also be used in constructing such tunable filters (e.g. low-pass, high-pass, band-pass, band-reject, notch, etc. . . . ). The person skilled in the art readily knows how to realize such tunable filters and how to select components with values (e.g. ranges of values) consistent with a desired filter characteristics (e.g. to provide a desired frequency response). Tuning of such tunable filter can comprise varying a value of one or more of its variable reactive elements under control of a signal-aware processor as discussed in the prior sections of the present disclosure.

As previously mentioned, the various exemplary embodiments of the present disclosure are not limited to a transmit path with an amplification stage comprising two amplifiers (150, 160), and transmit/receive systems with amplification stages in their transmit paths comprising more than two amplifiers can also benefit from the teachings of the present disclosure. According to an exemplary embodiment of the present disclosure, more than one, such as two or more, tunable filters (270) can be placed in various inter-stage locations of an amplification stage comprising more than two amplifiers (e.g. stages). Such configuration can allow attenuation of the transmit channel noise over a same frequency band corresponding to a receive signal at various points in the transmit path, with a net effect of reducing overall noise at the output of the transmit path. As the number of amplifier stages increases, amplification of the noise also increases, and therefore an increased number of filters (270) at various points of the transmit path can be desirable.

According to another embodiment of the present disclosure, the tunable filter (270) can be monolithically integrated with the driver (150) and/or with the final amplifier (160). Monolithic integration of the amplification stage (e.g. comprising driver (150) and final (160)) can be desirable because it provides, for example, matching between devices (e.g. transistors used in the amplifiers) to track and adjust variations due to manufacturing tolerances, temperature and others in ways not possible across multiple integrated circuits, such as, for example, described in the referenced U.S. patent application Ser. No. 13/797,779 and U.S. patent application Ser. No. 13/967,866, whose disclosures are incorporated herein by reference in their entirety. Other benefits of monolithic integration can include better overall performance of the integrated devices due to shorter traces as well as reduced manufacturing cost, assembly cost, testing cost and form factor. It follows that, according to an embodiment of the present disclosure, such monolithically integrated amplification stage (e.g. 150 and 160) can also include the (tunable) filter (270). Furthermore, a duplexer unit (130) comprising RLC filters such as per the relaxed design embodiments provided by the teaching according to the present disclosure, can also be monolithically integrated, entirely or partially, together with other components such as (150), (160) and (270) of the transmit/receive communication system (200) of FIG. 2. Latter monolithic integration of the duplexer unit is yet another benefit of not using a SAW/BAW filter in the design of the duplexer unit provided by the present teachings. Although the system diagram of FIG. 2 only shows a driver (150), a final (160), a filter (270) and a duplexer tilter (130) as part of a transmit path of the system (200), other components may be part of such transmit path, such as, for example, tunable match circuits and/or variable harmonic terminations, which can also partially or entirely be monolithically integrated with the driver (150), the final (160) and the filter (270). Tunable match circuits are described, for example, in the referenced U.S. patent application Ser. No. 13/967,866 and U.S. patent application Ser. No. 14/042,312, and variable harmonic terminations are described, for example, in the U.S. patent application Ser. No. 13/797,686, whose disclosures are incorporated herein by reference in their entirety.

The examples set forth above are provided to give those of ordinary skill in the art a complete disclosure and description of how to make and use the embodiments of the present disclosure, and are not intended to limit the scope of what the inventors regard as their disclosure. Modifications of the above described modes for carrying out the disclosure may be used by persons of skill in the art, and are intended to be within the scope of the following claims. All patents and publications mentioned in the specification may be indicative of the levels of skill of those skilled in the art to which the disclosure pertains. All references cited in this disclosure are incorporated by reference to the same extent as if each reference had been incorporated by reference in its entirety individually.

It is to be understood that the disclosure is not limited to particular methods or systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used in this specification and the appended claims, the singular forms “a”. “an”, and “the” include plural referents unless the content clearly dictates otherwise. The term “plurality” includes two or more referents unless the content clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains.

A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims. 

1. A radio frequency (RF) circuital arrangement comprising: an RF transmit path comprising: a plurality of cascaded amplifiers configured, during operation of the circuital arrangement, to amplify a transmit RF signal, the transmit RF signal operating over a first frequency band, and a first filter placed between two consecutive amplifiers of the plurality of cascaded amplifiers, the first filter configured during operation of the circuital arrangement, to attenuate a second frequency band different from the first frequency band, and pass the first frequency band: an RF receive path configured, during operation of the circuital arrangement, to receive a receive RF signal over the second frequency band, and a bi-directional transmit/receive circuit connected to the RF transmit path and to the RF receive path, the bi-directional transmit/receive circuit comprising: a second filter configured, during operation of the circuital arrangement, to pass the first frequency band and to attenuate the second frequency band.
 2. The RF circuital arrangement of claim 1, wherein: an attenuation over the first frequency band provided by the first filter is less than about 5 dB, and an attenuation over the second frequency band provided by the first filter is greater than about 10 dB.
 3. The RF circuital arrangement of claim 1 or claim 2, wherein an attenuation over the second frequency band provided by the combination of the first filter and the second filter is greater than about 35 dB.
 4. The RF circuital arrangement of claim 1, wherein, during operation of the circuital arrangement, the hi-directional transmit/receive circuit is configured: to provide an amplified version of the transmit RF signal from the RF transmit path to a transmit/receive antenna, and to receive the receive RF signal from the transmit/receive antenna and provide said signal to the RF receive path.
 5. The RF circuital arrangement of claim 1, wherein the first frequency band and the second frequency band are in correspondence of a mode of operation of the circuital arrangement, and wherein the circuital arrangement is configured, during operation of the circuital arrangement, to operate in one of a plurality of modes of operation comprising a plurality of different first frequency band and second frequency band.
 6. The RF circuital arrangement of claim 5, wherein the first filter is a tunable tilter configured, during operation of the circuital arrangement, to be tuned to attenuate a second frequency band and pass a first frequency band in correspondence of a mode of operation of the plurality of modes of operation of the circuital arrangement.
 7. The RF circuital arrangement of claim 6, wherein the first filter and the second filter are RLC type filters.
 8. The RF circuital arrangement of claim 6, wherein the first tilter is an RLC type filter.
 9. The RF circuital arrangement of claim 3, wherein the first filter and the second filter are RLC type filters.
 10. The RF circuital arrangement of claim 1, wherein the first filter comprises one or more of: a) a digitally tunable capacitor, and b) a digitally tunable inductor.
 11. The RF circuital arrangement of claim 7, wherein the first filter comprises one or more of: a) a digitally tunable capacitor, and b) a digitally tunable inductor.
 12. The RF circuital arrangement of claim 7, wherein the first filter is one of: a) a low-pass filter, b) a high-pass filter, c) a band-pass filter, d) a band-stop filter, and e) a notch filter.
 13. The RF circuital arrangement of claim 1, wherein the first filter is one of: a) a low-pass filter, b) a high-pass filter, c) a band-pass filter, d) a band-stop filter, and e) a notch filter.
 14. The RF circuital arrangement of any one of claims 1, 2, or 7, wherein the bi-directional transmit/receive circuit is a duplexer circuit comprising the second filter, and wherein the second filter is designed with relaxed parameters, wherein the relaxed parameters reduce a number of filter stages of the second filter.
 15. The RF circuital arrangement of claim 14, wherein the reduced number of filter stages of the second filter provide a reduced attenuation of the second filter in the first frequency band.
 16. The RF circuital arrangement of claim 15, wherein the reduced attenuation of the second filter in the first frequency band is less than about 2 dB.
 17. The RF circuital arrangement of claim 14, wherein the duplexer circuit further comprises a third filter coupled to the receive path and configured, during operation of the circuital arrangement, to pass the second frequency band.
 18. The RF circuital arrangement of claim 1, wherein the plurality of cascaded amplifiers and the first filter are monolithically integrated.
 19. The RF circuital arrangement of claim 7, wherein the plurality of cascaded amplifiers and the first and/or second filter are monolithically integrated.
 20. The circuital arrangement of claim 9, wherein the plurality of cascaded amplifiers and the first and/or second filter are monolithically integrated.
 21. The RF circuital arrangement of claim 1, wherein the plurality of cascaded amplifiers comprises a first amplifier configured to receive the RF transmit signal into the plurality of cascaded amplifiers, and a last amplifier configured to output an amplified version of the RF transmit signal by the plurality of cascaded amplifiers, and wherein the first filter is configured to attenuate an amplified noise figure at the second frequency band.
 22. The RF circuital arrangement of claim 1, further comprising one or more filters similar to the first filter, the one or more filters placed between one or more two consecutive amplifiers of the plurality of amplifiers, the one or more filters and the first filter not being directly connected, wherein the one or more filters are configured during operation of the circuital arrangement, to attenuate the second frequency band and pass the first frequency band.
 23. The RF circuital arrangement of claim 1, wherein the plurality of cascaded amplifiers comprises a driver amplifier and a final amplifier, and wherein the first filter is placed between the driver amplifier and the final amplifier.
 24. A communication device for bi-directional transmit and receive of RF signals, the communication device comprising the RF circuital arrangement of claim
 6. 25. The communication device of claim 24 further comprising a transceiver unit, wherein during operation of the communication device, the transceiver unit is adapted to tune the tunable filter according to the mode of operation.
 26. A method for reducing loss of a transmit RF signal in a duplexer unit of an radio frequency (RF) transmit/receive system, the method comprising: providing an RF transmit path comprising a plurality of cascaded amplifiers; inserting, in-between two amplifiers of the plurality of cascaded amplifiers, a first filter; based on the inserting, attenuating a receive frequency band and passing a transmit frequency band: based on the attenuating, relaxing design parameters of a second filter of a duplexer unit, the second filter being configured to pass the transmit frequency band and to attenuate the receive frequency band; based on the relaxing, reducing a number of filter stages of the second filter, and based on the reducing, reducing an attenuation at the transmit frequency band through the second filter of the duplexer unit.
 27. The method of claim 26, wherein the plurality of cascaded amplifiers comprises two amplifiers; a driver amplifier and a final amplifier, and wherein the first filter is inserted between the driver amplifier and the final amplifier.
 28. The method of claim 0 or claim 27, further comprising: coupling the second filter of the duplexer unit at an output of the plurality of cascaded amplifiers of the RF transmit path; based on the coupling, isolating an RF receive path operating at the receive frequency band from a signal at the output of the plurality of cascaded amplifiers, the RF receive path being coupled to a third filter of the duplexer unit, and based on the coupling, reducing an attenuation of a transmit RF signal via the RF transmit path.
 29. The method of claim 28, wherein the duplexer unit is coupled to a transmit/receive antenna, and wherein the duplexer unit is configured to receive an RF signal at the receive frequency hand and feed said RF signal to the RF receive path.
 30. The method of claim 28, wherein the third filter is configured to pass the receive frequency band and to attenuate the transmit frequency band.
 31. The method of claim 26, wherein the first filter is a tunable filter.
 32. The method of claim 31, further comprising: selecting a different receive frequency band and transmit frequency band, and based on the selecting, tuning the first filter to attenuate the different receive frequency band and pass the different transmit frequency band, wherein the second filter is configured to pass the different transmit frequency band and attenuate the different receive frequency band.
 33. The method of claim 32, wherein the selecting is in correspondence of a desired mode and/or channel of operation from a plurality of modes and/or channels of operation of the RF transmit/receive system, and wherein the second filter is configured to pass a plurality of transmit frequency hands and attenuate a plurality of receive frequency bands in correspondence of the plurality of modes and/or channels of operation of the RF transmit/receive system.
 34. The method of claim 32, wherein the tuning is performed by a controller unit aware of the different receive and transmit frequency bands.
 35. The method of claim 34, wherein the selecting and the tuning is performed by a transceiver unit of the RF transmit/receive system.
 36. The RF circuital arrangement of claim 26, wherein the second filter is an RLC type filter.
 37. The RF circuital arrangement of claim 26, wherein the first and the second filter are RLC type filters.
 38. The RF circuital arrangement of claim 31, wherein the first filter comprises one or more of: a) a digitally tunable capacitor, and b) a digitally tunable inductor.
 39. The RF circuital arrangement of claim 37, wherein the first filter is one of: a) a low-pass filter, b) a high-pass filter, c) a band-pass filter, d) a band-stop filter, and e) a notch filter. 